A spontaneous transplantable mammary carcinomia was discovered in guinea pigs. Hybridomas have been produced (by immunizing BALB/c mice) which react in a livecell RIA to the tumor cells and not to syngeneic guinea pig spleen and liver cells. After extensive characterization by numerous normal & tumor-derived guinea pig cells and by immunochemical techniques, the selected MoAbs will be used directly in immunotherapy trials and after conjugation to various drugs and toxins (i.e. daunomycin, ricin, etc.). Attempts are underway to put this tumor into culture. Spontaneous metastases formed in guinea pigs and MoAb to tumor metastasis will be developed and may prove to be more useful than MoAb to the primary tumor.